Clostridium difficile (C. difficile) is the most common cause of nosocomial diarrhea and accounts for about 3 million cases of diarrhea annually in the United States. The known risk factors of C. difficile infection (CDI) are exposure to antibiotics, advanced age, and residence in hospitals or long-term care facilities. The symptoms of CDI range from mild diarrhea to pseudomembranous colitis and toxic megacolon. The average cost of treatment is about $10,000 per case. The mortality rate of Clostridium difficile associated disease (CDAD) increased from 5.7 deaths per million population in 1999 to 23.7 deaths per million population in 2004 due to the emergence of hypervirulent outbreak strains. Accurate diagnosis is crucial for prompt and proper treatment of patients with CDI.